Systems and methods to recover value-added materials from gypsum

Abstract

Disclosed herein are systems and methods from processing flue gas desulfurization (FGD) gypsum feedstock and ash feedstocks, either separately or together. FGD gypsum conversion comprises reacting FGD gypsum (calcium sulfate) feedstock or phosphogypsum, in either batch or continuous mode, with ammonium carbonate reagent to produce commercial products comprising ammonium sulfate and calcium carbonate. A process to separate the impurities and convert the calcium carbonate to a pure precipitated calcium carbonate is disclosed. These impurities include a concentrate of valuable Rare Earth Elements, and radioactive thorium and uranium. A process to convert calcium sulfite to calcium sulfate using oxygen and a catalyst is also disclosed. Ash conversion comprises a leach process followed by a sequential precipitation process to selectively precipitate products at predetermined pHs resulting in metal hydroxides which may be converted to oxides or carbonates. The processes may be controlled by use of one or more processors.

What is claimed is: 
     
       1. A method for isolating metals from chemical processing comprising:
 forming a mixture comprising chemical intermediates, wherein the 
 chemical intermediates comprise at least one of calcium, nitrates, carbonates, sulfates and metal impurities wherein the mixture results from chemical processing, and wherein the mixture has a pH value; 
 responsive to forming the mixture, combining the mixture and a first reagent to change the pH of the mixture, wherein the first reagent is added until the pH of the mixture reaches a first predetermined pH value to form a first precipitate, wherein the first precipitate comprises at least one of a metal and a rare earth element; and 
 responsive to forming a precipitate, removing the precipitate from the mixture via a filter to form a first filtrate, 
 wherein the process to form the first precipitate is performed at a pH of 4, and wherein the first precipitate comprises at least one of iron, aluminum, uranium, scandium, or thorium. 
 
     
     
       2. The method of  claim 1 , further comprising:
 responsive to forming a first filtrate combining the first filtrate and a second reagent to change the pH of the first filtrate, wherein a second reagent is added until the pH of the first filtrate reaches a second predetermined pH value to form a second precipitate, wherein the second precipitate comprises at least one of a metal and a rare earth element; and 
 responsive to forming the second precipitate, removing the second precipitate from the first filtrate to form a second filtrate. 
 
     
     
       3. The method of  claim 1 , further comprising:
 responsive to forming a first filtrate combining the first filtrate and a second reagent to change the pH of the first filtrate, wherein a second reagent is added until the pH of the first filtrate reaches a second predetermined pH value to form a second precipitate, wherein the second precipitate comprises at least one of a metal and a rare earth element; 
 responsive to forming the second precipitate, removing the second precipitate from the first filtrate to form a second filtrate; 
 responsive to forming the second filtrate, combining the second filtrate and a third reagent to change the pH of the second filtrate, wherein the third reagent is added until the pH of the second filtrate reaches a third predetermined pH value to form a third precipitate, wherein the third precipitate comprises at least one of a metal and a rare earth element; and 
 responsive to forming a precipitate, removing the precipitate from the second filtrate to form a third filtrate. 
 
     
     
       4. The method of  claim 1 , wherein the chemical process comprises at least one of phosphogypsum processing, phosphate processing, coal fly ash processing, and red mud processing. 
     
     
       5. The method of  claim 1 , wherein the predetermined pH value is at least one of 4, 9, 11, and 13. 
     
     
       6. The method of  claim 1 , further comprising:
 responsive to forming a first filtrate combining the first filtrate and a reagent to change the pH of the first filtrate, wherein a second reagent is added until the pH of the first filtrate reaches a second predetermined pH value, wherein the second predetermined pH value is at least one of 4, 9, 11, and 13, to form a second precipitate, wherein the second precipitate comprises at least one of a metal and a rare earth element; and 
 responsive to forming the second precipitate, removing the second precipitate from the first filtrate to form a second filtrate. 
 
     
     
       7. The method of  claim 1 , further comprising:
 responsive to forming a first filtrate combining the first filtrate and a reagent to change the pH of the first filtrate, wherein a second reagent is added until the pH of the first filtrate reaches a second predetermined pH value, wherein the second predetermined pH value is at least one of 4, 9, 11, and 13, to form a second precipitate, wherein the second precipitate comprises at least one of a metal and a rare earth element; 
 responsive to forming the second precipitate, removing the second precipitate from the first filtrate to form a second filtrate; 
 responsive to forming the second filtrate, combining the second filtrate and a third reagent to change the pH of the second filtrate, wherein the third reagent is added until the pH of the second filtrate reaches a third predetermined pH value wherein the third predetermined pH value is at least one of 4, 9, 11, and 13, to form a third 
 precipitate, wherein the third precipitate comprises at least one of a metal and a rare earth element; and 
 responsive to forming a precipitate, removing the precipitate from the second filtrate to form a third filtrate. 
 
     
     
       8. The method of  claim 1  wherein the reagent is a base. 
     
     
       9. The method of  claim 1 , wherein the reagent is a base, and wherein the base is at least one of sodium hydroxide, calcium hydroxide, potassium hydroxide, ammonium hydroxide, and calcium carbonate. 
     
     
       10. The method of  claim 1 , further comprising concentrating the precipitated scandium and aluminum into a rare-earth mischmetal. 
     
     
       11. A system for isolating metals in a chemical process comprising:
 a mixture comprising chemical intermediates, wherein the chemical 
 intermediates comprise at least one of calcium, nitrates, carbonates, sulfates and metal impurities wherein the mixture results from chemical processing, and wherein the mixture has a pH; 
 a first reactor to combine the mixture and a first reagent to change the pH of the mixture, wherein the first reagent is added until the pH of the mixture reaches a first predetermined pH value to form a first precipitate, wherein the first precipitate comprises at least one of a metal and a rare earth element; and 
 a first filter to remove the first precipitate from the first mixture, wherein the remaining liquid is a first filtrate, 
 wherein the first predetermined pH is 4, and wherein the first precipitate comprises at least one of iron, aluminum, uranium, scandium or thorium. 
 
     
     
       12. The system of  claim 11 , further comprising:
 a second reactor to combine the first filtrate and a second reagent to change the 
 pH of the mixture, wherein the second reagent is added until the pH of the first filtrate reaches a first predetermined pH value to form a second precipitate, wherein the second precipitate comprises at least one of a metal and a rare earth element; and 
 a second filter to remove the second precipitate from the first filtrate, wherein the remaining liquid is a second filtrate. 
 
     
     
       13. The system of  claim 11 , further comprising:
 a second reactor to combine the first filtrate and a second reagent to change the 
 pH of the first filtrate, wherein the second reagent is added until the pH of the first filtrate reaches a second predetermined pH value to form a second precipitate, wherein the second precipitate comprises at least one of a metal and a rare earth element; 
 a second filter to remove the second precipitate from the first filtrate, wherein the remaining liquid is a second filtrate; 
 a third reactor to combine the second filtrate and a third reagent to change the pH of the second filtrate, wherein the third reagent is added until the pH of the first 
 filtrate reaches a third predetermined pH value to form a third precipitate, wherein the third precipitate comprises at least one of a metal and a rare earth element; and 
 a third filter to remove the third precipitate from the second filtrate, wherein the remaining liquid is a third filtrate. 
 
     
     
       14. The system of  claim 11 , wherein the chemical process comprises at least one of phosphogypsum processing, phosphate processing, coal fly ash processing, and red mud processing. 
     
     
       15. The system of  claim 11 , wherein the predetermined pH value is at least one of 4, 9, 11, and 13. 
     
     
       16. The system of  claim 11 , further comprising:
 a second reactor to combine the first filtrate and a second reagent to change the 
 pH of the mixture, wherein the second reagent is added until the pH of the first filtrate reaches a first predetermined pH value to form a second precipitate, wherein the second predetermined pH value is at least one of 4, 9, 11, and 13, wherein the second precipitate comprises at least one of a metal and a rare earth element; and 
 a second filter to remove the second precipitate from the first filtrate, wherein the remaining liquid is a second filtrate. 
 
     
     
       17. The system of  claim 11 , further comprising:
 a second reactor to combine the first filtrate and a second reagent to change the 
 pH of the first filtrate, wherein the second reagent is added until the pH of the first filtrate reaches a second predetermined pH value to form a second precipitate, wherein the second precipitate comprises at least one of a metal and a rare earth element; 
 a second filter to remove the second precipitate from the first filtrate, wherein the remaining liquid is a second filtrate; 
 a third reactor to combine the second filtrate and a third reagent to change the pH of the second filtrate, wherein the third reagent is added until the pH of the first filtrate reaches a third predetermined pH value to form a third precipitate, wherein the third predetermined pH value is at least one of 4, 9, 11, and 13, wherein the third precipitate comprises at least one of a metal and a rare earth element; and 
 a third filter to remove the third precipitate from the second filtrate, wherein the remaining liquid is a third filtrate. 
 
     
     
       18. The system of  claim 11 , wherein the first reagent is a base. 
     
     
       19. The system of  claim 11 , wherein the first reagent is a base, and wherein the base is at least one of sodium hydroxide, calcium hydroxide, potassium hydroxide ammonium hydroxide, and calcium carbonate.